Syringe cylinders of the kind in question here are known. They have an interior space comprising a stopper, which delimits an active ingredient space toward the outside. The active ingredient space may comprise an air bubble, which can expand and contract during temperature fluctuations, and particularly during pressure fluctuations, during air transport of the syringe cylinder. Due to pressure differences, the stopper in the interior space of the syringe cylinder may be displaced. In this process, it may reach regions of the interior space that are not, or not sufficiently, sterile. During a return displacement of the stopper due to a change in temperature, or in the event of a pressure drop, the active ingredient space may thus become contaminated. In order to be able to determine whether the stopper has been shifted beyond a maximum permitted range before employing a syringe cylinder, and before using a drug accommodated in the active ingredient space, it is necessary to determine the range traveled by the stopper. It is known to provide the interior space of a syringe cylinder on the side of a stopper facing away from the active ingredient space with graphite powder. The graphite powder adhering to the inside wall of the syringe cylinder is shifted as the stopper is displaced, so that upon a return displacement of the stopper a powder-free region of the inside wall of the syringe cylinder becomes visible. In order to be able to detect a displacement of the stopper, for example during air transport, in conventional syringe cylinders the region free from graphite powder has been determined. Starting with a certain width of this region, measured in the longitudinal direction of the syringe cylinder, it was safe to assume that the stopper had reached regions of the interior space that were not, or not sufficiently, sterilized and that the active ingredient space could be contaminated. It was then possible to sort such syringe cylinders.
It has been shown that the friction forces between the stopper and inside wall of the syringe cylinder were modified by the graphite powder. This possibly resulted in falsified measurement results. In addition, the graphite powder was able to travel back to the region over which the stopper passed during a shift. As a result, it was not detectable with certainty whether a stopper in fact had reached non-sterile regions or not.